RESULTS: Researchers at Harvard University have made several small mechanical devices powered by heart muscle harvested from rats. The creations include pumps, a device that “walks,” and one that swims.

WHY IT MATTERS: The scientists made the machines to study the behavior of muscles and to provide a platform for testing heart drugs. (The devices provide an easy way to monitor the effect of drugs on heart tissue.) Eventually, they could be used in new types of robots that can change shape, grip objects, and propel themselves.

METHODS: The researchers used a fabrication method called spin coating to make ultrathin elastic films; then they applied patterns of proteins to the films. Finally, they added heart-muscle cells; guided by the protein patterns, the cells organized themselves into working muscle tissue. To make the various devices, the researchers cut the muscular thin films into specific shapes (such as a triangle that resembled a fish’s tail) and changed the alignment of the cells. The devices, which must remain in a solution that keeps the muscles alive, can be controlled by electronic signals sent through the solution.

NEXT STEPS: The researchers are working to create devices that use human muscle tissue, perhaps grown from stem cells; such devices could be used in drug testing or to patch damaged heart muscle. So far, the muscle tissue survives for only a few weeks. For robotics applications, the scientists may combine heart muscle with other types of cells to increase longevity.